In this section we discuss our newly developed formalism for
handling of loop tensorial integrals in \(D\)  dimensions
using an orthogonal basis of external momenta.
As we stressed in Introduction we develop analytic method for
evaluation of one-loop diagrams with its further application to QCD
processes at fixed target regime (DY and SIDIS processes, prompt photon and
heavy flavor production, etc.). Our method can be extended to arbitrary number of legs in one-loop
diagrams and for both massless and massive particles. Development of analytical methods for study of
QCD processes is very important for understanding of their different aspects: angular distributions,
spin effects, access to the parton distributions. It is also important for performing resummation of large
logarithms, verifying of different identities (like Lam-Tung relation) involving hadronic structure functions,
behavior of the hadronic amplitudes at different kinematical limits and their expansions in small parameters
(like small transverse momentum of photon, etc.).
See, e.g., discussion in Refs. [1]}, [2]}.
